In 1843, Stark was invited by the Land and Water Power Company of Manchester to enter its service, make surveys, and superintend the building of the lower canal. This work was finished in the same year in which it was begun. The following season we find him engaged on surveys for the Vermont Central, and subsequently on the Old Colony Railroad, where he first served as assistant, and afterwards as resident engineer, in which position he remained until the completion of the work in 1845. From this period to the year 1847 he was in the service of his old friend and employer, Mr. Boyden, engaged on surveys and drawings for mill-work. At the close of his engagement with Mr. Boyden, Stark returned to Manchester and spent a good part of the season in making surveys and drawing a map of the compact part of the city, with reference to drainage. He also made a survey, accompanied with a report, upon the feasibility of supplying the city with water from Massabesic lake. The success of the new lines of railroad in New Hampshire stimulated interest in this form of investment, and several new roads and extensions were projected. The Nashua & Wilton and Stony Brook lines were the first lateral roads built, as feeders to the trunk roads of the Merrimack valley, and Stark was appointed chief engineer of both. On the completion of these lines, the Boston, Concord, & Montreal road, which had been built from Concord to Sanbornton, was extended northward, and the post of chief engineer was offered to Stark. His health failing in the summer of 1849, while engaged in this work, he left business cares and spent several months in recuperation, accepting, in the autumn of the same year, the situation of treasurer and assistant superintendent of the Nashua & Lowell Railroad, then under the management of Judge Charles F. Gove. This position was held until the early part of 1852, when he received the high compliment of an appointment as superintendent of the Hudson River Railroad. He had been in this position but little more than a year when an urgent offer was made to him to take the office vacated by the resignation of Judge Gove, the superintendent of the Nashua & Lowell Railroad and its branches. This position, being more congenial than that of the New York road, was accepted, and he entered upon the duties of his new situation at once.